Iggy Azaleais hosting the new incarnation of MTV's resuscitated House of Style, on which Jennifer Lopez will appear on one episode in Versace's Beverly Hills store discussing all things fashion. But you might be surprised to learn who the bigger diva was, according to an observer who was on set on Aug. 9.

"Iggy walked in with her entourage and wouldn't take her sunglasses off the whole time we were in the store shooting her," a production source tells THR. "She had a complete scowl the whole time and never cracked a smile — unless the cameras were on. And the minute they stopped, it was back to scowling."

The source adds that when the shoot moved outdoors to Via Rodeo, where fans had gathered, the Aussie rapper, 24, still wouldn't flash any teeth.

Meanwhile, says the source, "J.Lo was all smiles, saying hello to everyone on the crew, shaking everyone's hand and doing everything we needed her to do."

Azalea's rep could not be reached for comment.

This story first appeared in the Aug. 22 issue of The Hollywood Reporter magazine.